The invention relates to a high voltage overvoltage prevention circuit.
High voltage and deflection generating systems utilized in television receivers include the type disclosed in U.S. Pat. No. 3,452,244, which utilizes a trace switch to couple a deflection winding and a primary winding of a high voltage transformer across a source of energy during a trace interval of each deflection cycle and a commutating switch to supply replenishing energy to the source of energy during a commutating interval of each deflection cycle.
The signals developed on various secondary windings of the high voltage transformer are normally of predominantly one polarity during each deflection cycle. A high voltage multiplier and rectifier coupled to a first secondary winding of the high voltage transformer provides for multiplication and rectification of the signal on the first secondary winding, thereby providing an appropriate magnitude high voltage for the ultor anode of the kinescope tube. Other secondary windings provide signals to signal circuits of the television receiver to provide synchronization between deflection and the signal circuits.
When a failure of the trace switch or the circuitry which provides control of the trace switch occurs, the signals developed by the secondary windings of the high voltage transformer have nearly equal amplitude positive and negative maximum excursions. With this abnormal signal condition on the secondary windings, the multiplier and rectifier coupled to the first secondary winding creates an over-voltage condition at the ultor electrode of the kinescope (i.e., nearly one and one-half times the normal magnitude of high voltage). This over-voltage condition can result in damage to the kinescope. Also, the abnormal polarity conditions on other secondary windings may result in damage to signal circuits of the television receiver.